Methods for etch of SiN films

ABSTRACT

A method of selectively etching silicon nitride from a substrate comprising a silicon nitride layer and a silicon oxide layer includes flowing a fluorine-containing gas into a plasma generation region of a substrate processing chamber and applying energy to the fluorine-containing gas to generate a plasma in the plasma generation region. The plasma comprises fluorine radicals and fluorine ions. The method also includes filtering the plasma to provide a reactive gas having a higher concentration of fluorine radicals than fluorine ions and flowing the reactive gas into a gas reaction region of the substrate processing chamber. The method also includes exposing the substrate to the reactive gas in the gas reaction region of the substrate processing chamber. The reactive gas etches the silicon nitride layer at a higher etch rate than the reactive gas etches the silicon oxide layer.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/679,242 filed Apr. 6, 2015, now U.S. Pat. No. 9,343,327,which is a continuation of U.S. patent application Ser. No. 13/416,277filed Mar. 9, 2012, now U.S. Pat. No. 8,999,856, which claims thebenefit of U.S. Provisional Application No. 61/452,575, filed Mar. 14,2011, the contents of which are hereby incorporated by reference intheir entirety for all purposes.

The present application is also related to U.S. Nonprovisional patentapplication Ser. No. 13/088,930, filed Apr. 18, 2011, now U.S. Pat. No.9,324,576; Ser. No. 13/251,663, filed Oct. 3, 2011, now abandoned; andU.S. Nonprovisional patent application No. 13/416,223, filed Mar. 9,2012, now U.S. Pat. No. 9,064,815; the contents of which are eachincorporated herein by reference in their entirety for all purposes.

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned layers of materials on substrate surfaces.Producing patterned material on a substrate requires controlled methodsfor removal of exposed materials. Chemical etching is used for a varietyof purposes including transferring a pattern in photoresist intounderlying layers, thinning layers, or increasing lateral dimensions offeatures already present on the surface. Often it is desirable to havean etch process which etches one material faster than another. Such anetch process is said to be selective to the first material. As a resultof the diversity of materials, circuits, and processes, etch processeshave been developed with a selectivity towards a variety of materials.

Plasma deposition and etching processes for fabricating semiconductorintegrated circuits have been in wide use for decades. These processestypically involve the formation of a plasma from gases that are exposedto electric fields of sufficient power inside the processing chamber tocause the gases to ionize. The temperatures needed to form these plasmascan be much lower than needed to thermally ionize the same gases. Thus,plasma generation processes can be used to generate reactive radical andion species at significantly lower chamber processing temperatures thanis possible by simply heating the gases. This allows the plasma todeposit and/or etch materials from substrate surfaces without raisingthe substrate temperature above a threshold that will melt, decompose,or otherwise damage materials on the substrate.

Exemplary plasma deposition processes include plasma-enhanced chemicalvapor deposition (PECVD) of dielectric materials such as silicon oxideon exposed surfaces of a substrate wafer. Conventional PECVD involvesthe mixing of gases and/or deposition precursors in the processingchamber and striking a plasma from the gases to generate reactivespecies that react and deposit material on the substrate. The plasma istypically positioned close to the exposed surface of the substrate tofacilitate the efficient deposition of the reaction products.

Similarly, plasma etching processes include exposing selected parts ofthe substrate to plasma activated etching species that chemically reactand/or physically sputter materials from the substrate. The removalrates, selectivity, and direction of the plasma etched materials can becontrolled with adjustments to the etchant gases, plasma excitationenergy, and electrical bias between the substrate and charged plasmaspecies, among other parameters. Some plasma techniques, such ashigh-density plasma chemical vapor deposition (HDP-CVD), rely onsimultaneous plasma etching and deposition to deposit films on thesubstrate.

While plasma environments are generally less destructive to substratesthan high-temperature deposition environments, they still createfabrication challenges. Etching precision can be a problem withenergetic plasmas that over-etch shallow trenches and gaps. Energeticspecies in the plasmas, especially ionized species, can create unwantedreactions in a deposited material that adversely affect the material'sperformance. Thus, there is a need for systems and methods to providemore precise control over the plasma components that make contact with asubstrate wafer during fabrication.

SUMMARY

Systems and methods are described for improved control of theenvironment between a plasma and the surfaces of a substrate wafer thatare exposed to plasma and/or its effluents. The improved control may berealized at least in part by an ion suppression element positionedbetween the plasma and the substrate that reduces or eliminates thenumber of ionically-charged species that reach the substrate. Adjustingthe concentration of ion species that reach the substrate surface allowsmore precise control of the etch rate, etch selectivity, and depositionchemistry (among other parameters) during a plasma assisted etch and/ordeposition on the substrate.

In an embodiment, a method of selectively etching silicon nitride from asubstrate comprising a silicon nitride layer and a silicon oxide layeris provided. The method includes flowing a fluorine-containing gas intoa plasma generation region of a substrate processing chamber, andapplying energy to the fluorine-containing gas to generate a plasma inthe plasma generation region. The plasma comprises fluorine radicals andfluorine ions. The method also includes filtering the plasma to providea reactive gas having a higher concentration of fluorine radicals thanfluorine ions, and flowing the reactive gas into a gas reaction regionof the substrate processing chamber. The method also includes exposingthe substrate to the reactive gas in the gas reaction region of thesubstrate processing chamber. The reactive gas etches the siliconnitride layer at a higher etch rate than the reactive gas etches thesilicon oxide layer.

In another embodiment, an etch process providing a higher etch rate ofsilicon nitride than an etch rate of silicon oxide is provided. Theprocess includes generating a plasma from a fluorine-containing gas. Theplasma comprises fluorine radicals and fluorine ions. The process alsoincludes removing a portion of the fluorine ions from the plasma toprovide a reactive gas having a higher concentration of fluorineradicals than fluorine ions, and exposing a substrate comprising asilicon nitride layer and a silicon oxide layer to the reactive gas. Thereactive gas etches the silicon nitride layer at a higher etch rate thanthe reactive gas etches the silicon oxide layer.

Additional embodiments and features are set forth in part in thedescription that follows and will become apparent to those skilled inthe art upon examination of the specification or may be learned by thepractice of the invention. The features and advantages of the inventionmay be realized and attained by means of the instrumentalities,combinations, and methods described in the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings, wherein like reference numerals are usedthroughout the several drawings to refer to similar components. In someinstances, a sub-label is associated with a reference numeral andfollows a hyphen to denote one of multiple similar components. Whenreference is made to a reference numeral without specifying an existingsub-label, it is intended to refer to all such multiple similarcomponents.

FIG. 1 shows a simplified cross-sectional view of a processing systemthat includes a processing chamber having a capacitively coupled plasma(CCP) unit and a showerhead according to an embodiment of the invention;

FIG. 2 shows a simplified perspective view of a processing system thatincludes a processing chamber having a CCP unit and a showerheadaccording to an embodiment of the invention;

FIG. 3 shows a simplified schematic of the gas flow paths of a pair ofgas mixtures through a processing system according to an embodiment ofthe invention;

FIG. 4 shows a simplified cross-sectional view of a processing systemthat includes a processing chamber having a showerhead that also acts asan ion suppression element according to an embodiment of the invention;

FIG. 5 shows a simplified cross-sectional view of a processing systemthat includes a processing chamber with an ion suppression platepartitioning a plasma region from a gas reaction region according to anembodiment of the invention;

FIG. 6A shows a simplified perspective view of an ion-suppressionelement according to an embodiment of the invention;

FIG. 6B shows a simplified perspective view of a showerhead that alsoacts as an ion-suppression element according to an embodiment of theinvention;

FIG. 7A shows some exemplary hole geometries for openings in anion-suppression element according to an embodiment of the invention;

FIG. 7B shows a schematic of a hole geometry for an opening in anion-suppression element according to an embodiment of the invention;

FIG. 8 shows an exemplary configuration of opposing openings in a pairof electrodes that help define a plasma region in a processing chamberaccording to an embodiment of the invention;

FIG. 9 is a simplified flowchart illustrating an exemplary method ofselectively etching silicon nitride from a substrate comprising asilicon nitride layer and a silicon oxide layer according to anembodiment of the invention; and

FIG. 10 is a simplified flowchart illustrating an exemplary etch processproviding a higher etch rate of silicon nitride than an etch rate ofsilicon oxide according to an embodiment of the invention.

DETAILED DESCRIPTION

Systems and methods are described for the generation and control of aplasma inside a semiconductor processing chamber. The plasma mayoriginate inside the processing chamber, outside the processing chamberin a remote plasma unit, or both. Inside the chamber, the plasma iscontained and separated from the substrate wafer with the help of an ionsuppression element that is positioned between the plasma and thesubstrate wafer. In some instances, this ion suppression element mayalso function as part of a plasma generation unit (e.g., an electrode),a gas/precursor distribution system (e.g., a showerhead), and/or anothercomponent of the processor system. In additional instances, the ionsuppression element may function primarily to define a partition betweena plasma generation region and a gas reaction region that etches and/ordeposits material on exposed surfaces of the substrate wafer.

The ion suppression element functions to reduce or eliminate ionicallycharged species traveling from the plasma generation region to thesubstrate. Uncharged neutral and radical species may pass through theopenings in the ion suppressor to react at the substrate. It should benoted that complete elimination of ionically charged species in thereaction region surrounding the substrate is not always the desiredgoal. In many instances, ionic species are required to reach thesubstrate in order to perform the etch and/or deposition process. Inthese instances, the ion suppressor helps control the concentration ofionic species in the reaction region at a level that assists theprocess.

Exemplary Processing System Configurations

Exemplary processing system configurations include an ion suppressorpositioned inside a processing chamber to control the type and quantityof plasma excited species that reach the substrate. In some embodimentsthe ion suppressor unit may be a perforated plate that may also act asan electrode of the plasma generating unit. In additional embodimentsthe ion suppressor may be the showerhead that distributes gases andexcited species to a reaction region in contact with the substrate. Instill more embodiments ion suppression may be realized by a perforatedplate ion suppressor and a showerhead, both of which plasma excitedspecies pass through to reach the reaction region.

FIGS. 1 and 2 show simplified cross-sectional and perspective views,respectively, of a processing system that includes both an ionsuppressor 110 as part of a capacitively coupled plasma (CCP) unit 102and a showerhead 104 that may also contribute to ion suppression. Theprocessing system may also optionally include components located outsidethe processing chamber 100, such as fluid supply system 114. Theprocessing chamber 100 may hold an internal pressure different than thesurrounding pressure. For example, the pressure inside the processingchamber may be about 1 mTorr to about 100 Torr.

The CCP unit 102 may function to generate a plasma inside the processingchamber 100. The components of the CCP unit 102 may include a lid or hotelectrode 106 and an ion suppression element 110 (also referred toherein as an ion suppressor). In some embodiments, the lid 106 and ionsuppressor 110 are electrically conductive electrodes that can beelectrically biased with respect to each other to generate an electricfield strong enough to ionize gases between the electrodes into aplasma. An electrical insulator 108, may separate the lid 106 and theion suppressor 110 electrodes to prevent them from short circuiting whena plasma is generated. The plasma exposed surfaces of the lid 106,insulator 108, and ion suppressor 110 may define a plasma excitationregion 112 in the CCP unit 102.

Plasma generating gases may travel from a gas supply system 114 througha gas inlet 116 into the plasma excitation region 112. The plasmagenerating gases may be used to strike a plasma in the excitation region112, or may maintain a plasma that has already been formed. In someembodiments, the plasma generating gases may have already been at leastpartially converted into plasma excited species in a remote plasmasystem (not shown) positioned outside the processing chamber 100 beforetraveling downstream though the inlet 116 to the CCP unit 102. When theplasma excited species reach the plasma excitation region 112, they maybe further excited in the CCP unit 102, or pass through the plasmaexcitation region without further excitation. In some operations, thedegree of added excitation provided by the CCP unit 102 may change overtime depending on the substrate processing sequence and/or conditions.

The plasma generating gases and/or plasma excited species may passthrough a plurality of holes (not shown) in lid 106 for a more uniformdelivery into the plasma excitation region 112. Exemplary configurationsinclude having the inlet 116 open into a gas supply region 120partitioned from the plasma excitation region 112 by lid 106 so that thegases/species flow through the holes in the lid 106 into the plasmaexcitation region 112. Structural and operational features may beselected to prevent significant backflow of plasma from the plasmaexcitation region 112 back into the supply region 120, inlet 116, andfluid supply system 114. The structural features may include theselection of dimensions and cross-sectional geometry of the holes in lid106 that deactivates back-streaming plasma, as described below withreference to FIGS. 7A and 7B. The operational features may includemaintaining a pressure difference between the gas supply region 120 andplasma excitation region 112 that maintains a unidirectional flow ofplasma through the ion suppressor 110.

As noted above, the lid 106 and the ion suppressor 110 may function as afirst electrode and second electrode, respectively, so that the lid 106and/or ion suppressor 110 may receive an electric charge. In theseconfigurations, electrical power (e.g., RF power) may be applied to thelid 106, ion suppressor 110, or both. For example, electrical power maybe applied to the lid 106 while the ion suppressor 110 is grounded. Thesubstrate processing system may include a RF generator 140 that provideselectrical power to the lid 106 and/or ion suppressor 110. Theelectrically charged lid 106 may facilitate a uniform distribution ofplasma (i.e., reduce localized plasma) within the plasma excitationregion 112. To enable the formation of a plasma in the plasma excitationregion 112, insulator 108 may electrically insulate lid 106 and ionsuppressor 110. Insulator 108 may be made from a ceramic and may have ahigh breakdown voltage to avoid sparking. The CCP unit 102 may furtherinclude a cooling unit (not shown) that includes one or more coolingfluid channels to cool surfaces exposed to the plasma with a circulatingcoolant (e.g., water).

The ion suppressor 110 may include a plurality of holes 122 thatsuppress the migration of ionically-charged species out of the plasmaexcitation region 112 while allowing uncharged neutral or radicalspecies to pass through the ion suppressor 110 into an activated gasdelivery region 124. These uncharged species may include highly reactivespecies that are transported with less reactive carrier gas through theholes 122. As noted above, the migration of ionic species through theholes 122 may be reduced, and in some instances completely suppressed.Controlling the amount of ionic species passing through the ionsuppressor 110 provides increased control over the gas mixture broughtinto contact with the underlying wafer substrate, which in turnincreases control of the deposition and/or etch characteristics of thegas mixture. For example, adjustments in the ion concentration of thegas mixture can significantly alter its etch selectivity (e.g.,SiNx:SiOx etch ratios, metal:SiOx etch ratios, metal:SiNx etch ratios,Poly-Si:SiOx etch ratios, etc.). It can also shift the balance ofconformal-to-flowable of a deposited dielectric material.

The plurality of holes 122 may be configured to control the passage ofthe activated gas (i.e., the ionic, radical, and/or neutral species)through the ion suppressor 110. For example, the aspect ratio of theholes (i.e., the hole diameter to length) and/or the geometry of theholes may be controlled so that the flow of ionically-charged species inthe activated gas passing through the ion suppressor 110 is reduced. Theholes in the ion suppressor 110 may include a tapered portion that facesthe plasma excitation region 112, and a cylindrical portion that facesthe showerhead 104. The cylindrical portion may be shaped anddimensioned to control the flow of ionic species passing to theshowerhead 104. An adjustable electrical bias may also be applied to theion suppressor 110 as an additional means to control the flow of ionicspecies through the suppressor.

The showerhead 104 is positioned between the ion suppressor 110 of theCCP unit 102 and a gas reaction region 130 (i.e., gas activation region)that makes contact with a substrate that may be mounted on a pedestal150. The gases and plasma excited species may pass through the ionsuppressor 110 into an activated gas delivery region 124 that is definedbetween the ion suppressor 110 and the showerhead 104. A portion ofthese gases and species may further pass thorough the showerhead 104into a gas reaction region 130 that makes contact with the substrate.

The showerhead may be a dual-zone showerhead that has a first set ofchannels 126 to permit the passage of plasma excited species, and asecond set of channels that deliver a second gas/precursor mixture intothe gas reaction/activation region 130. The two sets of channels preventthe plasma excited species and second gas/precursor mixture fromcombining until they reach the gas reaction region 130. In someembodiments, one or more of the holes 122 in the ion suppressor 110 maybe aligned with one or more of the channels 126 in the showerhead 104 toallow at least some of the plasma excited species to pass through a hole122 and a channel 126 without altering their direction of flow. Inadditional embodiments, the second set of channels may have an annularshape at the opening facing the gas reaction region 130, and theseannular openings may be concentrically aligned around the circularopenings of the first set of channels 126.

The second set of channels in the showerhead 104 may be fluidly coupledto a source gas/precursor mixture (not shown) that is selected for theprocess to be performed. For example, when the processing system isconfigured to perform a deposition of a dielectric material such assilicon dioxide (SiO_(x)) the gas/precursor mixture may include asilicon-containing gas or precursor such as silane, disilane, TSA, DSA,TEOS, OMCTS, TMDSO, among other silicon-containing materials. Thismixture may react in gas reaction region 130 with an oxidizing gasmixture that may include plasma excited species such as plasma generatedradical oxygen (O), activated molecular oxygen (O₂), and ozone (O₃),among other species. Excessive ions in the plasma excited species may bereduced as the species move through the holes 122 in the ion suppressor110, and reduced further as the species move through the channels 126 inthe showerhead 104. In another example, when the processing system isconfigured to perform an etch on the substrate surface, the sourcegas/precursor mixture may include etchants such as oxidants, halogens,water vapor and/or carrier gases that mix in the gas reaction region 130with plasma excited species distributed from the first set of channelsin the showerhead 104.

The processing system may further include a power supply 140electrically coupled to the CCP unit 102 to provide electric power tothe lid 106 and/or ion suppressor 110 to generate a plasma in the plasmaexcitation region 112. The power supply may be configured to deliver anadjustable amount of power to the CCP unit 102 depending on the processperformed. In deposition processes, for example, the power delivered tothe CCP unit 102 may be adjusted to set the conformality of thedeposited layer. Deposited dielectric films are typically more flowableat lower plasma powers and shift from flowable to conformal when theplasma power is increased. For example, an argon containing plasmamaintained in the plasma excitation region 112 may produce a moreflowable silicon oxide layer as the plasma power is decreased from about1000 Watts to about 100 Watts or lower (e.g., about 900, 800, 700, 600,or 500 Watts or less), and a more conformal layer as the plasma power isincreased from about 1000 Watts or more (e.g., about 1000, 1100, 1200,1300, 1400, 1500, 1600, 1700 Watts or more). As the plasma powerincreases from low to high, the transition from a flowable to conformaldeposited film may be relatively smooth and continuous or progressthrough relatively discrete thresholds. The plasma power (either aloneor in addition to other deposition parameters) may be adjusted to selecta balance between the conformal and flowable properties of the depositedfilm.

The processing system may still further include a pedestal 150 that isoperable to support and move the substrate (e.g., a wafer substrate).The distance between the pedestal 150 and the showerhead 104 help definethe gas reaction region 130. The pedestal may be vertically or axiallyadjustable within the processing chamber 100 to increase or decrease thegas reaction region 130 and effect the deposition or etching of thewafer substrate by repositioning the wafer substrate with respect to thegases passed through the showerhead 104. The pedestal 150 may have aheat exchange channel through which a heat exchange fluid flows tocontrol the temperature of the wafer substrate. Circulation of the heatexchange fluid allows the substrate temperature to be maintained atrelatively low temperatures (e.g., about −20° C. to about 90° C.).Exemplary heat exchange fluids include ethylene glycol and water.

The pedestal 150 may also be configured with a heating element (such asa resistive heating element) to maintain the substrate at heatingtemperatures (e.g., about 90° C. to about 1100° C.). Exemplary heatingelements may include a single-loop heater element embedded in thesubstrate support platter that makes two or more full turns in the formof parallel concentric circles. An outer portion of the heater elementmay run adjacent to a perimeter of the support platen, while an innerportion may run on the path of a concentric circle having a smallerradius. The wiring to the heater element may pass through the stem ofthe pedestal.

FIG. 3 shows a simplified schematic of the gas flow paths of a pair ofgas mixtures through a processing system that includes both an ionsuppressor plate and a showerhead. At block 305, a first gas, such as aplasma generating gas mixture, is supplied to the processing chamber viaa gas inlet. The first gas may include one or more of the followinggases: CF₄, NH₃, NF₃, Ar, He, H₂O, H₂, O₂, etc. Inside the processingchamber, the first gas may be excited through a plasma discharge to formone or more plasma effluents at block 310. Alternatively (or in additionto the in-situ plasma generation), a remote plasma system (RPS) coupledto the processing chamber may be used to generate an ex-situ plasmawhose plasma excitation products are introduced into the processchamber. The RPS plasma excitation products may includeionically-charged plasma species as well as neutral and radical species.

Whether the plasma effluents are generated by an in-situ plasma unit, anRPS unit, or both, they may be passed through an ion suppressor in theprocessing chamber at block 315. The ion suppressor may block and/orcontrol the passage of ionic species while allowing the passage ofradical and/or neutral species as the plasma activated first gas travelsto the gas reaction region in the processing chamber. At block 320, asecond gas may be introduced into the processing chamber. As notedabove, the contents of the second gas depend on the process performed.For example, the second gas may include deposition compounds (e.g.,Si-containing compounds) for deposition processes and etchants for etchprocesses. Contact and reaction between the first and second gases maybe prevented until the gases arrive at the gas reaction region of theprocess chamber.

One way to prevent the first and second gases from interacting beforethe gas reaction region is to have them flow though separate channels ina dual-zone showerhead (DZSH). Block 330 shows the activated first gasand second gas passing through a DZSH 33 that has a first plurality ofchannels that permit the activated first gas to pass through theshowerhead without interacting with the second gas that passes through asecond plurality of channels. After exiting the DZSH, the first andsecond gases may mix together in the gas reaction region of theprocessing chamber at block 335. Depending on the process performed, thecombined gases may react to deposit a material on the exposed surfacesof the substrate, etch materials from the substrate, or both.

Referring now to FIG. 4, a simplified cross-sectional view of aprocessing system 400 having a showerhead 428 that also acts as an ionsuppression element is shown. In the configuration shown, a first gassource 402 for plasma generation is fluidly coupled to an optional RPSunit 404 where a first plasma may be generated and the plasma effluentstransported into the processing chamber 406 through gas inlet 408.Inside the processing chamber 406, the gases may pass through holes 410in a gas distribution plate 412 into a gas region 414 defined betweenthe plate 412 and showerhead 428. In some embodiments, this region 414may be a plasma excitation/activation region where the gas distributionplate 412 and showerhead 428 act as first and second electrodes tofurther excite the gas and/or generate the first plasma. The holes 410in the gas distribution plate 412 may be dimensionally or geometricallystructured to deactivate back-streaming plasma. The plate 412 andshowerhead 428 may be coupled with a RF power generator 422 thatsupplies a charge to the plate 412 and showerhead 428 to excite thegases and/or generate a plasma. In one embodiment, the showerhead 428 isgrounded while a charge is applied to plate 412.

The excited gases or activated gases in the gas region 414 may passthrough showerhead 428 into a gas reaction region 416 adjacent asubstrate 418 to etch material from the surface of the substrate and/ordeposit material on the substrate's surface. The showerhead 428 may be aDZSH that allows the excited gases to pass from the gas region 414 intothe gas reaction region 416 while also allowing a second gas (i.e.,precursor gas/mixture) to flow from an external source (not shown) intothe gas reaction region 416 via a second gas inlet 426. The DZSH mayprevent the activated/excited gas from mixing with the second gas untilthe gases flow into the gas reaction region 416.

The excited gas may flow through a plurality of holes 424 in the DZSH,which may be dimensionally and/or geometrically structured to control orprevent the passage of plasma (i.e., ionically charged species) whileallowing the passage of activated/excited gases (i.e., reactive radicalor uncharged neutral species). FIG. 7A provides exemplary embodiments ofhole configurations that may be used in the DZSH. In addition to theholes 424, the DZSH may include a plurality of channels 426 throughwhich the second gas flows. The second gas (precursor gas) may exit theshowerhead 428 through one or more apertures (not shown) that arepositioned adjacent holes 424. The DZSH may act as both a second gasdelivery system and an ion suppression element.

As described above, the mixed gases may deposit a material on and/oretch a material from the surface of the substrate 418, which may bepositioned on a platen 420. The platen 420 may be vertically movablewithin the processing chamber 406. The processing of the substrate 418within the processing chamber 406 may be affected by the configurationsof the holes 424, the pressure within the gas region 414, and/or theposition of the substrate 418 within the processing chamber. Further,the configuration of the holes 424 and/or pressure within the gas region414 may control the concentration of ionic species (plasma) allowed topass into the gas excitation region 416. The ionic concentration of thegas mixture can shift the balance of conformal-to-flowable of adeposited dielectric material in addition to altering the etchselectivity.

Referring now to FIG. 5, a simplified cross-sectional view of anotherprocessing system 500 having a plate 512 (i.e., ion suppressor plate)that acts as an ion suppression element is shown. In the configurationshown, a first gas source 502 is fluidly coupled to an RPS unit 504where a first plasma may be generated and the plasma effluentstransported into the processing chamber 506 through gas inlet 508. Theplasma effluents may be transported to a gas region 514 defined betweenthe ion suppressor plate 512 and the gas inlet 508. Inside the gasregion 514, the gases may pass through holes 510 in the ion suppressor512 into a gas reaction/activation region 516 defined between the ionsuppressor 512 and a substrate 518. The substrate 518 may be supportedon a platen 520 as described above so that the substrate is movablewithin the processing chamber 506.

Also as described above, the holes 510 may be dimensionally and/orgeometrically structured so that the passage of ionically chargedspecies (i.e., plasma) is prevented and/or controlled while the passageof uncharged neutral or radical species (i.e., activated gas) ispermitted. The passage of ionic species may be controllable by varyingthe pressure of the plasma within gas region 514. The pressure in gasregion 514 may be controlled by controlling the amount of gas deliveredthrough gas inlet 508. The precursor gas (i.e., second gas) may beintroduced into the processing chamber 506 at one or more second gasinlets 522 positioned vertically below or parallel with ion suppressor512. The second gas inlet 522 may include one or more apertures, tubes,etc. (not shown) in the processing chamber 506 walls and may furtherinclude one or more gas distribution channels (not shown) to deliver theprecursor gas to the apertures, tubes, etc. In one embodiment, the ionsuppressor 512 includes one or more second gas inlets, through which theprecursor gas flows. The second gas inlets of the ion suppressor 512 maydeliver the precursor gas into the gas reaction region 516. In such anembodiment, the ion suppressor 512 functions as both an ion suppressorand a dual zone showerhead as described previously. The activated gasthat passes through the holes 510 and the precursor gas introduced inthe processing chamber 506 may be mixed in the gas reaction chamber 516for etching and/or deposition processes.

Having now described exemplary embodiments of processing chambers,attention is now directed to exemplary embodiments of ion suppressors,such as ion suppressor plates 412 and 512 and showerhead 428.

Exemplary Ion Suppressors

FIG. 6A shows a simplified perspective view of an ion-suppressionelement 600 (ion suppressor) according to an embodiment of theinvention. The ion suppression element 600 may correspond with the ionsuppressor plates of FIG. 4 and/or FIG. 5. The perspective view showsthe top of the ion suppression element or plate 600. The ion suppressionplate 600 may be generally circular shaped and may include a pluralityof plasma effluent passageways 602, where each of the passageways 602includes one or more through holes that allow passage of the plasmaeffluents from a first region (e.g., plasma region) to a second region(e.g., gas reaction region or showerhead). In one embodiment, thethrough holes of the passageway 602 may be arranged to form one or morecircular patterns, although other configurations are possible. Asdescribed previously, the through holes may be geometrically ordimensionally configured to control or prevent the passage of ionspecies while allowing the passage or uncharged neutral or radicalspecies. The through holes may have a larger inner diameter toward thetop surface of the ion suppression plate 600 and a smaller innerdiameter toward the bottom surface of the ion suppression plate.Further, the through holes may be generally cylindrical, conical, or anycombination thereof. Exemplary embodiments of the configurations of thethrough holes are provided in FIGS. 7A-B.

The plurality of passageways may be distributed substantially evenlyover the surface of the ion suppression plate 600, which may provideeven passage of neutral or radical species through the ion suppressionplate 600 into the second region. In some embodiments, such as theembodiment of FIG. 5, the processing chamber may only include an ionsuppression plate 600, while in other embodiments, the processingchamber may include both a ion suppression plate 600 and a showerhead,such as the showerhead of FIG. 6B, or the processing chamber may includea single plate that acts as both a dual zone showerhead and an ionsuppression plate.

FIG. 6B shows a simplified bottom view perspective of a showerhead 620according to an embodiment of the invention. The showerhead 620 maycorrespond with the showerhead illustrated in FIG. 4. As describedpreviously, the showerhead 620 may be positioned vertically adjacent toand above a gas reaction region. Similar to ion suppression plate 600,the showerhead 620 may be generally circular shaped and may include aplurality of first holes 622 and a plurality of second holes 624. Theplurality of first holes 622 may allow plasma effluents to pass throughthe showerhead 620 into a gas reaction region, while the plurality ofsecond holes 624 allow a precursor gas, such as a silicon precursor,etchants etc., to pass into the gas reaction region.

The plurality of first holes 622 may be through holes that extend fromthe top surface of the showerhead 620 through the showerhead. In oneembodiment, each of the plurality of first holes 622 may have a smallerinner diameter (ID) toward the top surface of the showerhead 620 and alarger ID toward the bottom surface. In addition, the bottom edge of theplurality of first holes 622 may be chamfered 626 to help evenlydistribute the plasma effluents in the gas reaction region as the plasmaeffluents exit the showerhead and thereby promote even mixing of theplasma effluents and precursor gases. The smaller ID of the first holes622 may be between about 0.5 mm and about 20 mm. In one embodiment, thesmaller ID may be between about 1 mm and 6 mm. The cross sectional shapeof the first holes 622 may be generally cylindrical, conical, or anycombination thereof. Further, the first holes 622 may be concentricallyaligned with the through holes of passageways 602, when both an ionsuppression element 600 and a showerhead 620 are used in a processingchamber. The concentric alignment may facilitate passage of an activatedgas through both the ion suppression element 600 and showerhead 620 inthe processing chamber.

In another embodiment, the plurality of first holes 622 may be throughholes that extend from the top surface of the showerhead 620 through theshowerhead, where each of the first holes 622 have a larger ID towardthe top surface of the showerhead and a smaller ID toward the bottomsurface of the showerhead. Further, the first holes 622 may include ataper region that transitions between the larger and smaller IDs. Such aconfiguration may prevent or regulate the passage of a plasma throughthe holes while permitting the passage of an activated gas. Suchembodiments may be used in place of or in addition to ion suppressionelement 600. Exemplary embodiments of such through holes are provided inFIG. 7A.

The number of the plurality of first holes 622 may be between about 60and about 2000. The plurality of first holes 622 may also have a varietyof shapes, but are generally round. In embodiments where the processingchamber includes both a ion suppression plate 600 and a showerhead 620,the plurality of first holes 622 may be substantially aligned with thepassageways 602 to facilitate passage of the plasma effluents throughthe ion suppression plate and showerhead.

The plurality of second holes 624 may extend from the bottom surface ofthe showerhead 620 partially through the showerhead. The plurality ofsecond holes may be coupled with or connected to a plurality of channels(not shown) that deliver the precursor gas (e.g., deposition compounds,etchants, etc.) to the second holes 624 from an external gas source (notshown). The second holes may include a smaller ID at the bottom surfaceof the showerhead 620 and a larger ID in the interior of the showerhead.The number of second holes 624 may be between about 100 and about 5000or between about 500 and about 2000 in different embodiments. Thediameter of the second holes' smaller ID (i.e., the diameter of the holeat the bottom surface) may be between about 0.1 mm and about 2 mm. Thesecond holes 624 are generally round and may likewise be cylindrical,conical, or any combination thereof. Both the first and second holes maybe evenly distributed over the bottom surface of the showerhead 620 topromote even mixing of the plasma effluents and precursor gases.

With reference to FIG. 7A, exemplary configurations of the through holesare shown. The through holes depicted generally include a large innerdiameter (ID) region toward an upper end of the hole and a smaller IDregion toward the bottom or lower end of the hole. The smaller ID may bebetween about 0.2 mm and about 5 mm. Further, aspect ratios of the holes(i.e., the smaller ID to hole length) may be approximately 1 to 20. Suchconfigurations may substantially block and/or control passage of ionspecies of the plasma effluent while allowing the passage of radical orneutral species. For example, varying the aspect ratio may regulate theamount of plasma that is allowed to pass through the through holes.Plasma passage may further be regulated by varying the pressure of theplasma within a region directly above the through holes.

Referring now to specific configurations, through hole 702 may include alarge ID region 704 at an upper end of the hole and a small ID region706 at a lower end of the hole with a stepped edge between the large andsmall IDs. Through hole 710 may include a large ID region 712 on anupper end and a large ID region 716 on a lower end of the hole with asmall ID region 714 therebetween. The transition between the large andsmall ID regions may be stepped or blunt to provide an abrupt transitionbetween the regions.

Through hole 720 may include a large ID region 722 at the upper end ofthe hole and small ID region 726 at a lower end of the hole with atapered region 724 that transitions at an angle θ between the large andsmall regions. The height 728 of the small ID region 726 may depend onthe overall height 727 of the hole, the angle θ of tapered region 724,the large ID, and the small ID. In one embodiment, the tapered region724 comprises an angle of between about 15° and about 30°, andpreferably about 22°; the overall height 727 is between about 4 mm andabout 8 mm, and preferably about 6.35 mm; the large ID is between about1 mm and about 4 mm, and preferably about 2.54 mm; the small ID isbetween about 0.2 mm and 1.2 mm, and preferably about 0.89 mm, so thatthe height 728 of the small ID region 726 region is between about 1 mmand about 3 mm, and preferably about 2.1 mm.

Through hole 730 may include a first ID region 732 at the upper end ofthe hole, a second ID region 734 concentrically aligned with andpositioned vertically below first ID region 732, and a third ID region736 concentrically aligned with and positioned vertically below secondID region 734. First ID region 732 may comprise a large ID, second IDregion 734 may comprise a small ID, and third ID region 736 may comprisea slightly larger ID than second ID region 734. Third ID region 736 mayextend to the lower end of the hole or may be outwardly tapered to anexit ID 737. The taper between the third ID region 736 and the exit ID737 may taper at an angle θ₃, which may be between about 15° and about30°, and preferably about 22°. The second ID region 734 may include achamfered edge that transitions from the first ID region 732 at an angleθ₁, which may be between about 110° and about 140°. Similarly, thesecond ID region 734 may include a chamfered edge that transitions intothe third ID region 736 at an angle θ₂, which may also be between about110° and about 140°. In one embodiment, the large ID of first region 732may be between about 2.5 mm and about 7 mm, and preferably about 3.8 mm;the small ID of second ID region 734 may be between about 0.2 mm andabout 5 mm, and preferably about 0.4 mm; the slightly larger ID of thirdID region 736 may be between about 0.75 mm and about 2 mm, andpreferably about 1.1 mm; and the exit ID may be between about 2.5 mm andabout 5 mm, and preferably about 3.8 mm.

The transition (blunt, stepped, tapered, etc.) between the large IDregions and small ID regions may substantially block the passage of ionspecies from passing through the holes while allowing the passage ofradical or neutral species. For example, referring now to FIG. 7B, shownis an enlarged illustration of through hole 720 that includes thetransition region 724 between the large ID region 722 and the small IDregion 726. The tapered region 724 may substantially prevent plasma 725from penetrating through the through hole 720. For example, as theplasma 725 penetrates into the through hole 720, the ion species maydeactivate or ground out by contacting the walls of the tapered region724, thereby limiting the passage of the plasma through the through holeand containing the plasma within the region above the through hole 720.The radical or neutral species, however, may pass through the throughhole 720. Thus, the through hole 720 may filter the plasma 720 toprevent or control the passage of unwanted species. In an exemplaryembodiment, the small ID region 726 of the through holes comprises an IDof 1 mm or smaller. To maintain a significant concentration of radicaland/or neutral species penetrating through the through holes, the lengthof the small ID region and/or the taper angle may be controlled.

In addition to preventing the passage of plasma, the through holesdescribed herein may be used to regulate the passage of plasma so that adesired level of plasma is allowed to pass through the through hole.Regulating the flow of plasma through the through holes may includeincreasing the pressure of the plasma in the gas region above the ionsuppressor plate so that a desired fraction of the plasma is able topass through the ion suppressor without deactivating or grounding out.

Referring now to FIG. 8, a simplified illustration of a CCP unit 800 isshown. Specifically, the CCP unit 800 shown includes a top plate 802 anda bottom plate 804 that define a plasma generation region 810 in which aplasma is contained. As previously described, the plasma may begenerated by an RPS (not shown) and delivered to the plasma generationregion 810 via through hole 806. Alternatively or additionally, theplasma may be generated in the CCP unit 800, for example, by utilizingtop plate 802 and bottom plate 804 as first and second electrodescoupled to a power generation unit (not shown).

The top plate 802 may include a through hole 806 that allows process gasand/or plasma to be delivered into the plasma generation region 810while preventing back-streaming of plasma through the top plate 802. Thethrough hole 806 may be configured similar to through hole 730 havingfirst, second, and third ID regions (820, 822, and 824 respectively),with a chamfered edge between adjacent regions (828 and 829) and atapered region 826 transitioning between third ID region 824 and an exitID. The tapered region 826 between third ID region 824 and the exit IDand/or the chamfered edge between second and third ID regions (822 and824 respectively) may prevent back-streaming of plasma by deactivatingor grounding ion species as the plasma penetrates into the through hole806.

Similarly, the bottom plate 804 may include a through hole 808 thatallows the radical or neutral species to pass through the through holewhile preventing or controlling the passage of ion species. The throughhole 808 may be configured similar to through hole 720 having a large IDregion 830, a small ID region 832, and a tapered region 834 thattransitions between the large ID region 830 and the small ID region 832.The tapered region 834 may prevent the flow of plasma through thethrough hole 808 by deactivating or grounding ion species as previouslyexplained while allowing radical or neutral species to pass therethrough.

To further prevent passage of the plasma through the through holes, 806and/or 808, the top plate 802 and/or bottom plate 804 may receive acharge to electrically bias the plasma and contain the plasma withinplasma generation region 810 and/or adjust an ion concentration in theactivated gas that passes through the bottom plate. Using top plate 802and bottom plate 804 in CCP unit 800, the plasma may be substantiallygenerated and/or maintained in the plasma generation region 810, whileradical and neutral species are delivered to a gas reaction region to bemixed with one or more precursor gases to etch material from or depositmaterial on a substrate surface.

Exemplary Processes

In accordance with some embodiments of the invention, an ion suppressoras described above may be used to provide radical and/or neutral speciesfor etch or deposition processes. In one embodiment, for example, an ionsuppressor is used to provide fluorine radicals to selectively etchsilicon nitride. Using the fluorine radicals, an etch rate selectivityof silicon nitride to silicon oxide of as high as about 80:1 or more canbe obtained. One use for such a process is to remove silicon nitride ina replacement gate process. A silicon nitride gate may be selectivelyremoved without removing exposed silicon oxide regions such as gateoxide. The silicon nitride may be replaced with a gate material such asmetal.

The ion suppressor may be used to provide a reactive gas having a higherconcentration of radicals than ions. Because most of the chargedparticles of a plasma are filtered or removed by the ion suppressor, thesubstrate is typically not biased during the etch process. Such aprocess using radicals and other neutral species can reduce plasmadamage compared to conventional plasma etch processes that includesputtering and bombardment. Embodiments of the present invention arealso advantageous over conventional wet etch processes where surfacetension of liquids can cause bending and peeling of small features.

FIG. 9 is a simplified flowchart illustrating an exemplary method ofselectively etching silicon nitride from a substrate comprising asilicon nitride layer and a silicon oxide layer according to anembodiment of the invention. The method includes flowing afluorine-containing gas into a plasma generation region of a substrateprocessing chamber (902). The fluorine-containing gas may include HF,F₂, NF₃, CF₄, CHF₃, C₂F₆, C₃F₆, BrF₃, ClF₃, SF₆, or the like. Otherembodiments may include other halogen-containing gases that do notinclude fluorine, such as Cl₂, HBr, SiCl₄, and the like, in place of thefluorine-containing gas. In the exemplary method of FIG. 9, thefluorine-containing gas may also include one or more oxygen sources suchas O₂, O₃, N₂O, NO, or the like. Using oxygen can increase an etch rateof the silicon nitride with minimal impact on an etch rate of thesilicon oxide. The fluorine-containing gas may also include one or moreinert gases such as H₂, He, N₂, Ar, or the like. The inert gas can beused to improve plasma stability. Flow rates and ratios of the differentgases may be used to control etch rates and etch selectivity. In anembodiment, the fluorine-containing gas includes NF₃ at a flow rate ofbetween about 5 sccm and 500 sccm, O₂ at a flow rate of between about 0sccm and 5000 sccm, He at a flow rate of between about 0 sccm and 5000sccm, and Ar at a flow rate of between about 0 sccm and 5000 sccm. Oneof ordinary skill in the art would recognize that other gases and/orflows may be used depending on a number of factors including processingchamber configuration, substrate size, geometry and layout of featuresbeing etched, and the like.

The method also includes applying energy to the fluorine-containing gasto generate a plasma in the plasma generation region (904). As would beappreciated by one of ordinary skill in the art, the plasma may includea number of charged and neutral species including radicals and ions. Theplasma may be generated using known techniques (e.g., RF, capacitivelycoupled, inductively coupled, and the like). In an embodiment, theenergy is applied using a CCP unit at a source power of between about 15W and 5000 W and a pressure of between about 0.2 Torr and 30 Torr. TheCCP unit may be disposed remote from a gas reaction region of theprocessing chamber. For example, the CCP unit and the plasma generationregion may be separated from the gas reaction region by an ionsuppressor.

The method also includes filtering the plasma to provide a reactive gashaving a higher concentration of fluorine radicals than fluorine ions(906). The plasma may be filtered using an ion suppressor disposedbetween the plasma generation region and the gas reaction region of thesubstrate processing chamber. The ion suppressor may include a pluralityof channels that allow passage of the fluorine radicals and neutralspecies between the plasma generation region and the gas reactionregion. The ion suppressor may be configured to remove some or all ofthe ions passing from the plasma generation region. In an embodiment,for example, a significant portion of the ions may be removed such thatthe reactive gas is substantially free from ions.

The method also includes flowing the reactive gas into a gas reactionregion of the substrate processing chamber (908). In an embodiment, theion suppressor may be configured as a showerhead, and the reactive gasexiting the ion suppressor may flow into the gas reaction regionproximate to the substrate. Alternatively, the reactive gas exiting theion suppressor may flow through a showerhead or another gas distributorand into the gas reaction region.

The method also includes exposing the substrate to the reactive gas inthe gas reaction region of the substrate processing chamber (910). In anembodiment, the temperature of the substrate may be between about −10°C. and 200° C., and the pressure in the substrate processing chamber maybe between about 0.2 Torr and 30 Torr. One of ordinary skill in the artwould recognize that other temperatures and/or pressures may be useddepending on a number of factors as explained previously. The reactivegas etches the silicon nitride layer at a higher etch rate than thereactive gas etches the silicon oxide layer.

FIG. 10 is a simplified flowchart illustrating an exemplary etch processproviding a higher etch rate of silicon nitride than an etch rate ofsilicon oxide according to an embodiment of the invention. The processincludes generating a plasma from a fluorine-containing gas, the plasmacomprising fluorine radicals and fluorine ions (1002). As explainedabove, the plasma may be formed in a plasma generation region of asubstrate processing chamber that is separate from a gas reactionregion. The process also includes removing a portion of the fluorineions from the plasma to provide a reactive gas having a higherconcentration of fluorine radicals than fluorine ions (1004). Theportion of the fluorine ions may be removed using an ion suppressor. Theprocess also includes exposing a substrate comprising a silicon nitridelayer and a silicon oxide layer to the reactive gas, where the reactivegas etches the silicon nitride layer at a higher etch rate than thereactive gas etches the silicon oxide layer (1006).

It should be appreciated that the exemplary processes illustrated inFIGS. 9-10 are not limited to use with the processing chambersillustrated in FIGS. 1-5 or the ion-suppression elements illustrated inFIGS. 6A, 6B, 7A, 7B, and 8-9. Rather, processes in accordance withembodiments of the invention may be performed using other hardwareconfigurations. Further, the specific steps illustrated in FIGS. 9-10provide particular methods in accordance with embodiments of the presentinvention. The steps outlined above may be continuously repeated bysystem software, and other sequences of steps may be performed accordingto alternative embodiments. For example, the steps outlined above may beperformed in a different order. Moreover, the individual stepsillustrated in FIGS. 9-10 may include multiple sub-steps that may beperformed in various sequences as appropriate to the individual step.Furthermore, additional steps may be added or removed depending on theparticular application. One of ordinary skill in the art would recognizemany variations, modifications, and alternatives.

It should be noted that the methods and apparatuses discussed throughoutthe specification are provided merely as examples. Various embodimentsmay omit, substitute, or add various steps or components as appropriate.For instance, it should be appreciated that features described withrespect to certain embodiments may be combined in various otherembodiments. Furthermore, embodiments may be implemented by hardware,software, firmware, middleware, microcode, hardware descriptionlanguages, or any combination thereof. When implemented in software,firmware, middleware, or microcode, the program code or code segments toperform the necessary tasks may be stored in a computer-readable mediumsuch as a storage medium. Processors may be adapted to perform thenecessary tasks. The term “computer-readable medium” includes, but isnot limited to, portable or fixed storage devices, optical storagedevices, sim cards, other smart cards, and various other mediums capableof storing, containing, or carrying instructions or data.

What is claimed is:
 1. A method of etching a patterned substrate, themethod comprising: transferring the patterned substrate into a substrateprocessing region of a substrate processing chamber, wherein thepatterned substrate has exposed silicon nitride and exposed silicon;flowing a fluorine-containing precursor into a remote plasma regionfluidly coupled to the substrate processing region while forming aremote plasma in the remote plasma region to produce plasma effluents;flowing water vapor into the substrate processing region without firstpassing the water vapor through any remote plasma; and etching theexposed silicon nitride.
 2. The method of claim 1 wherein a selectivityof the operation (exposed silicon nitride: exposed silicon) is greaterthan or about 50:1.
 3. The method of claim 1 wherein the operation offorming the remote plasma comprises a remote plasma power between 25 Wand 500 W.
 4. The method of claim 1 wherein a pressure in the substrateprocessing region is between about 0.1 Torr and about 15 Torr during theoperation of etching the exposed silicon nitride.
 5. The method of claim1 wherein an electron temperature in the substrate processing region isless than 0.5 eV during the operation of etching the exposed siliconnitride.
 6. The method of claim 1 wherein plasma effluents pass throughan ion suppressor disposed between the remote plasma region and thesubstrate processing region.
 7. The method of claim 1 wherein thefluorine-containing precursor comprises NF₃.
 8. The method of claim 1wherein the fluorine-containing precursor comprises a precursor selectedfrom the group consisting of hydrogen fluoride, atomic fluorine,diatomic fluorine, and carbon tetrafluoride.
 9. The method of claim 1wherein a temperature of the patterned substrate is between about 25° C.and about 90° C. during the operation of etching the exposed siliconnitride.
 10. A method of etching a patterned substrate, the methodcomprising: transferring the patterned substrate into a substrateprocessing region of a substrate processing chamber, wherein thepatterned substrate has exposed silicon nitride and exposed silicon;flowing nitrogen trifluoride into a remote plasma region fluidly coupledto the substrate processing region while forming a remote plasma in theremote plasma region to produce plasma effluents; flowing water vaporinto the substrate processing region without first passing the watervapor through the remote plasma region; etching the exposed siliconnitride, wherein a temperature of the patterned substrate is betweenabout 40° C. and about 80° C. during the operation of etching theexposed silicon nitride; and removing the patterned substrate from thesubstrate processing region.